A nonsynchronous manufacturing system, employing standard fixturized work piece holding pallets which can be conveyed along a line, stopped, accurately located, rigidly clamped for a work operation, and released to proceed to a plurality of successive work stations for performing a plurality of sequential operations, is disclosed in U.S. Pat. No. RE.25,886 issued Oct. 26, 1965. The illustrated embodiment employs a vertical loop conveyor having a continuous chain drive with means for clutching and declutching the pallets at the operating stations on an upper level and with pallet return on a lower level.
The basic nonsynchronous system, with each work station operating independently of the others and with variable float of pallets between stations, has also been implemented in horizontal systems where a continuous chain conveyor drive is adapted to support and frictionally drive pallets which can be stopped and accurately located at successive stations. The configuration of such horizontal systems has generally been in the form of parallel lines joined by semi-circular ends with work stations confined to the straight line portions of the sytem.
A further modification of the basic nonsynchronous system is disclosed in U.S. Pat. No. 4,570,782 wherein a circular path conveyor is provided by means of a continuously rotating horizontal plate or ring. Here again the pallets proceed independently from station to station where they are stopped, located and clamped for the duration of the work operation and released for frictional drive to the next station independently of the other pallets which may cue up behind any pallet during its operation at the work station.
In horizontal chain drive installations, two types of chain conveyor have been employed each involving a roller chain and sprocket drive. In one, a single chain having vertical axis pivots is provided with relatively wide upper flat surface crescent plates each connected to a recessed pin of the roller chain to provide a smooth surface for frictional drive with the under surface of work piece loaded pallets. The upper surfaces of such crescent plates lie in the same plane with circular arc male and female crescent ends to accommodate horizontal articulation passing around curved paths. Laterally spaced dual chains of similar construction have also been employed with smaller crescent plates and links, both narrower and having shorter pitch, which have become standard for most applications and are preferred for use in the systems of the present application.